1. Field of the Invention
The present invention relates to a spindle motor used in a drive unit for a hard disc apparatus in a computer or the like, a DVD unit, a CD-RPM unit or the like, and to a method of manufacturing thereof. In particular, the present invention relates to a spindle motor having a hydrodynamic bearing structure as a drive motor for a thin hard disc drive apparatus installed in a portable personal computer such as a notebook type personal computer, and a method of manufacturing thereof.
2. Related Art
Conventionally, a bearing housing and a thrust bearing in a spindle motor have been coupled with each other by means of press-fitting, shrinkage-fitting, adhesive-bonding, welding or the like.
Further, there have been coupled with each other by a coupling method using a plastic deformation process as disclosed in JP-A-6-178491, or a coupling method using a tight coupling force caused by plastic flow as disclosed in JP-A-2000-81029.
However, the conventional coupling methods have caused the following problems in the case of joining a thrust bearing (having, for example, an outer diameter of 5 mm and a thickness of 1 mm) to a bearing housing of a spindle motor having a hydrodynamic bearing structure, for a 2.5 inch type thin hard disc apparatus:
As well-known, the press-fitting has a limited bonding strength, and in particular, it is inferior to shock-resistance. Further, the shrinkage fitting cannot ensure a sufficient shrinkage fitting margin since the bearing has a small diameter, and accordingly, it also has a limited bonding strength. Further, since the shrinkage fitting requires heating, accordingly, after shrinkage fitting, the degree of accuracy becomes inferior, and a finishing process is required after the joining thereof. Further, heating and cooling thereof are time-consuming, resulting in low productivity.
The adhesive bonding has a limited coupling strength since the bonding length is short, and accordingly, it is inferior to shock-resistance. Further, extra adhesive having oozed out from the juncture detrimentally affects the performance of the motor, and curing of an adhesive is time-consuming, resulting in low productivity.
The welding causes thermal deformation, and in particular causes a warp due to thermal-contraction. Thus, accuracy cannot be ensured. Further, a shaft made of a material having a martensitic structure with a high carbon content, such as SUS404C, causes cracking. Further, the welding requires an expensive facility such as a laser welder.
As to a joining method using a plastic deformation process as disclosed in JP-A-6-178491, in the case of plastic-deformation of a juncture over its entire periphery, corrugation (buckling) is caused in the plastically deformed zone, which would possibly cause external leakage of fluid from a bearing housing therethrough. Further, should the zone where plastic deformation is made be divided into several parts, the fluid would possibly leaks externally from the bearing housing through parts where no plastic deformation is made. Further, as an axially exerted load is applied in a cicumferentially discrete condition, inhomogeneous force is circumferentially exerted to the thrust bearing or the bearing housing which would be deformed so as to cause a risk of rotational oscillation of the shaft.
As a tight juncture forming method using the plastic flow disclosed in JP-A-2000-81029, it is required to enhance the bonding strength and to increase the working load in order to prevent leakage of fluid from the bearing housing, and accordingly, the radial bearing or the like would deform, resulting in lowering of the performance of the spindle motor.
An object of the present invention is to provided a spindle motor having an enhanced bonding strength of the juncture between the bearing housing and the thrust bearing with no deterioration of accuracy and sealing ability.
To the end, according to the present invention, there is provided a method comprising the steps of inserting or press-fitting an outer cylindrical portion of a thrust bearing having an annular inclined surface at the outer periphery of an axially end part thereof in an coupling bore formed in an end surface of a bearing housing, and pressing the end surface of the bearing housing around the coupling bore over its entire periphery of the latter, so as to allow plastic flow of the base material around the inner periphery of the coupling bore, and thereby, the annular inclined surface at the outer periphery of the end part is covered with the base material of the bearing housing which has been subjected to plastic flow. Thus, the thrust bearing and the bearing housing are coupled with each other so that the material of the bearing housing can obtain a shearing strength and a residual contact pressure after application of a compression load.
Specifically, according to a first aspect of the present invention which can achieve the above-mentioned purposes, there is provided a spindle motor including a stator core, and comprising, inside of the stator core, a cylindrical bearing housing, a hydrodynamic bearing metal and a shaft fixed at its one end to a hub, which are coaxially arranged in the mentioned order as viewed inward from the stator core, and also comprising a thrust bearing fixed to an inner peripheral surface at an end part of the bearing housing on the side remote from the hub, for bearing a thrust of the shaft, fluid being filled between the shaft and the hydrodynamic bearing metal, wherein an annular inclined surface is formed on an outer peripheral edge at an end part of the thrust bearing on the side axially remote from the hub, the annular inclined surface having an outer diameter which decreases toward the end part on the side axially remote from the hub, an inner peripheral edge at the end part of the bearing housing on the side axially remote from the hub is bulged out toward the inclined surface through plastic deformation so as to abut against and join with the latter.
According to a second aspect of the present invention which can achieve the above-mentioned purpose, there is provided a spindle motor including a stator core, and comprising, inside of the stator core, a cylindrical bearing housing, a hydrodynamic bearing metal and a shaft fixed at its one end to a hub, which are coaxially arranged in the mentioned order as viewed inward from the stator core, and also comprising a thrust bearing fixed to an inner peripheral surface at an end part of the bearing housing on the side remote from the hub, for bearing a thrust of the shaft, fluid being filled between the shaft and the hydrodynamic bearing metal, wherein an annular inclined surface is formed on an outer peripheral edge at the end part of the thrust bearing on the side axially remote from the hub, the annular inclined surface having an outer diameter which decreases toward the end part on the side axially remote from the hub, an inner peripheral edge of the end part of the bearing housing on the side axially remote the hub is bulged out toward the inclined surface so as to abut against and join with the latter, the bulged portion having a metal structure which is flatted in a direction along the outer surface of the bulged portion.
The inclined surface formed in the thrust bearing may have such a sectional shape in a cutting plane including the axis of the thrust bearing as to be of a straight line or a part of an arc.
Further, it is desirable that the inclined surface formed on the outer peripheral edge of the thrust bearing on the large diameter side is made into contact with the inner peripheral of the bearing housing.
Further, it is desirable that a part having a diameter smaller than that of the outer periphery of the thrust bearing is present in the bearing housing, coaxial therewith, and the thrust bearing is interposed between the plastically deformed part of the bearing housing and a stepped part at the end surfaced of the small diameter part of the thrust bearing, directly or through the intermediary of other members.
Further, according to a third aspect of the present invention which can achieve the above-mentioned problems, there is provided a method of manufacturing a spindle motor including a stator core, and comprising, inside of the stator core, a cylindrical bearing housing, a hydrodynamic bearing metal and a shaft fixed at its one end to a hub, which are coaxially arranged in the mentioned order as viewed inward from the stator core, and also comprising a thrust bearing fixed to an inner peripheral surface in an end part of the bearing housing on the side remote from the hub, for bearing a thrust of the shaft, fluid being filled between the shaft and the hydrodynamic bearing metal, comprising the steps of forming an annular inclined surface having a diameter which is decreased toward the end part on the side axially remote from the hub, on an outer peripheral edge of thrust bearing on the side axially remote from the hub, fitting the thrust bearing in the bearing housing up to a predetermined position, thereafter pressing the peripheral edge of the end part of the bearing housing on the side remote from the hub, simultaneously over its entire periphery in the axial direction so as to cause plastic flow of the inner peripheral edge which therefore bulges out over the inclined surface of the thrust bearing so as to abut against and join with the inclined surface.
In the above-mentioned manufacturing method, the annular inclined surface formed in the thrust bearing may have such a sectional shape so as to be of a straight line or a part of an arc in a cutting plane including the axis of the thrust bearing.
According to the present invention having the above-mentioned constructions, the juncture between the thrust bearing and the bearing housing has a sufficient bonding strength without deteriorating the accuracy and the sealing ability thereof, thereby it is possible to join the thrust bearing and the bearing housing with each other with a high degree of productivity using an inexpensive facility.
The present invention will be detailed in the form of preferred embodiments of the present invention with reference to the accompanying drawings in which: